Defined Benefit Pension and Other Postretirement Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 35
Pension settlement expenses	$ 2	$ 21	4	$ 90
Other Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefits paid			10
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefits paid			17
Pension settlement expenses	$ 0	$ 0	$ 0	$ 0